Sen. Lindsey Graham said Wednesday the FBI needs to stop stonewalling his request to clear up wiretapping claims President Trump made against his predecessor and produce evidence that it happened.

Graham said he originally thought Trump’s accusation that former President Obama tapped his phones at Trump Tower during last year’s presidential campaign was “just kind of a wild claim.” He has since sent the FBI a letter asking for proof.

“If it’s not true, just tell me it’s not true. Why is it taking so long to get the answer?” he told TODAY. “I have no evidence of it, I’m suspicious of it, but now I’m getting concerned because it’s taking so long to answer my letter.”

Graham warned that if the FBI fails to comply with his request, “Congress is going to flex its muscle” and use subpoena power to get the information.

He also supported fellow Sen. Chuck Grassley's threat to hold up Trump’s nomination for deputy attorney general, Rod Rosenstein, until Congress is briefed about potential ties between Russia and Trump.

Grassley chairs the Senate Judiciary Committee.

In the letter to the FBI and the Justice Department last week, Graham and Rhode Island Sen. Sheldon Whitehouse asked for any copies of warrants or court orders the Obama administration would have needed to authorize a bug on Trump's phones.

"I think the entire country needs to know ... if there’s something there," he said, adding later, "If there’s not, we need to put it to bed."

Graham also pointed out that James Clapper, the former director of national intelligence, has denied that any of Trump’s phones were tapped.

Separately, Graham criticized the Republican attempt to revamp the Affordable Care Act, calling the bill House Republicans proposed "mortally wounded" and expressing doubt it had enough votes to clear the Senate.

He suggested that Republicans let Obamacare collapse "under its own weight" and then challenge Democrats to help "fix a problem they created."

"We’re trying to do too much, too quick as Republicans,” Graham said, suggesting they instead “slow down, get it right.”